(Late to the party, but:) You may be interested in the active line of academic research into making "undetectable" hardware Trojans by subtly messing with circ

(Late to the party, but:) You may be interested in the active line of academic research into making "undetectable" hardware Trojans by subtly messing with circuits. It looks like http://asiaccs2017.com/slides/Paar.pdf http://asiaccs2017.com/slides/Paar.pdf (currently down, Google cache: http://webcache.googleusercontent.com/search?q=cache:kHlrZtaBvGEJ:asiaccs2017.com/slides/Paar.pdf+&cd=12&hl=en&ct=clnk&gl=nl&client=firefox-b http://webcache.googleusercontent.com/search?q=cache:kHlrZta...) is a good introduction.